Atmospheric ion is a collective term for fine particles that are electrically charged positively or negatively and suspended in the atmosphere. Of those, particles that carry a positive charge are called positive ions and particles that carry a negative charge are called negative ions.
Atmospheric ions are generated when gas molecules in the atmosphere are ionized. When particles in the atmosphere mainly composed of nitrogen molecules and oxygen molecules are given energy equivalent to their ionization energy, the particles release electrons and become initial positive ions. The released electrons react with other atmospheric particles to form initial negative ions.
These initial ions react with minor components of the atmosphere and assemble into nuclear ions. The nuclear ions further react with components of the atmosphere and bind to water molecules to form cluster ions.
A device which can artificially generate cluster ions readily and effectively is a negative ion generating device brought up herein.
In general, negative ion generating devices are largely divided into four types based on the way of generating ions; Leonard type, corona discharge type, electron emission type, and radioactive material type.
All the types have advantages and disadvantages. Among them, corona discharge type negative ion generating devices, which generate ions by forcibly applying a flow of oxygen molecules to electrons moving from one electrode to another using the ionizing effect of corona discharge, can be relatively compact and produced at low costs and can continuously generate a large amount of negative ions. Therefore, corona discharge type negative ion generating devices are used widely on its own or in combination with electric potential treatment instruments, health appliances, air purification systems, air conditioners and so on.
Electrons emission type negative ion generating devices generate negative ions of oxygen by supplying electrons generated by a discharge to oxygen molecules in the air. This type of ion generators has generally the same characteristics as the corona discharge type ion generators.
The corona discharge type and electron emission type negative ion generating devices are generally the same in that they have a discharging electrode and a high-voltage DC power source, and a negative high voltage (−3 to −9 KV, for example) from the high-voltage DC power source is applied to the discharging electrode and ionization by corona discharge is induced to generate negative ions although there is a slight difference in the structure of the electrode (see JP-A-2003-139342 (pp. 1 to 9 of the specification and FIGS. 1 to 5) and JP-A-2001-56395 (pp. 1 to 5 of the specification and FIGS. 1 to 9), for example).
The problems of such discharge type negative ion generating devices are how efficiently stable negative ions can be generated and how effectively the generated negative ions can be applied to a human body or the like. One method for improving the negative ion generation efficiency is to apply a driving voltage to the discharging electrode intermittently (see JP-A-2003-59622 (pp. 1 to 10 of the specification and FIGS. 1 to 31), for example).
Also, some electric potential treatment instruments and cosmetic or health appliances using negative ions have a charging means for charging a human body to a positive potential (or ground potential) in order to apply generated negative ions to the human body effectively.
To apply the generated negative ions intensively to a target such as human body with a charging means or the like produces high treatment effect and high heath promotion effect and has good practical use. However, such a charging means cannot be used in a negative ion generating device for releasing negative ions into indoor air used on its own or incorporated in an air purification system or air conditioner.
Thus, it is important to improve the negative ions generation efficiency itself. To improve the negative ion generation efficiency of a negative ion generating device leads to improvement of the negative ions concentration effect of the charging means.
In reality, however, the negative ion generation efficiency cannot be necessarily improved by driving a charging means intermittently with an intermittent drive means. On the contrary, such a charging means makes the control circuit on the power source side complex and results in an increase in production costs.